The present invention relates generally to aircraft emergency power generating systems and, more particularly, to ram air turbines utilized on aircraft to provide emergency power.
Auxiliary power units (APUs) are a necessary part of most commercial and military aircraft. APUs are designed to meet aviation power needs during ground operations, when the main engines are not running. APUs provide power for electrical and instrumentation systems, hydraulic systems, and main engine startup, and supply power to the environmental control system. More recently, aircraft have begun to use APUs not just for necessary ground operations but for in-flight functions. Thus, APUs are increasingly configured to operate as standalone sources of accessory power, independent of the main engines.
Regulations require that aircraft have an emergency power source that is independent of the primary power source(s). The emergency power source is necessary to control an aircraft's flight surfaces in the event of a loss of the primary power sources. Normally, a ram air turbine (RAT) is utilized to provide emergency power to an aircraft in the event of main engine failure. Typically, RATs are deployed from the mid-fuselage, forward fuselage, or under wing of an aircraft. When a RAT is deployed, air rushing past the aircraft due to the aircraft's forward speed causes the turbine blades to spin. The power generated by the spinning turbine can be utilized to drive electric generators and hydraulic pumps to supply the aircraft with emergency power. Conventional RATs utilize a mechanical governor to vary the blade pitch of the turbine. The power output of the turbine changes with the blade pitch, thereby controlling the operating speed of the turbine. The RAT assembly and the mechanical governor are expensive, complex, and increase the system level mass of the emergency power system.